The present invention relates to microwave tank-contents level measuring systems, and more particularly to the assemby to be mounted and to its mounting on the exterior of a tank over an opening in the tank top wall.
In U.S. Pat. No. 4,044,355, issued Aug. 23, 1977, there is described a microwave based system for measuring the contents of tanks, such as oil or the like in the tanks of a tanker vessel. A source of microwave energy is mounted externally over an opening at the highest point in the tank. The assemably is illustrated and described as consisting of an upright tubular capsule [housing], in the upper portion of which is mounted a bowl-shaped downwardly concave antenna. A smaller tubular capsule [housing], mounted horizontally on one side of the first capsule, houses a microwave generator and mixers. A waveguide projects from the generator and mixers into the upright larger capsule and carries at its inner end a microwave horn spaced below and coaxial with the antenna. The horn is directed upwardly illuminating the antenna which radiates a signal downwardly toward the surface whose level is to be determined. Returning echo signals are collected by the antenna and directed back to the horn and then to the mixers for processing and determination of the level of the tank contents. Access or service covers are located above the upright capsule and at the free end of the horizontal capsule. Details are presented for the electronics required to complete the system, but because the electronics constitute no part of the present invention, they will not be discussed further.
As mentioned above, the source of microwave energy is mounted externally over an opening in the tank. That is, the bottom of the upright capsule is provided with a flange for joining the assembly to the exterior of a tank top. As shown in the patent drawings, the upright capsule is cylindrical with its bottom end completely open and mounted over a circular opening in the tank wall which opening has a diameter slightly smaller than that of the upright capsule.
The aforesaid patented apparatus has a serious drawback. When the measuring assembly is mounted on a tank, the entire interiors of the capsules and their contents are exposed to the atmosphere present in the tank. The fumes from crude oil or other petroleum products can be corrosive and attack the components of the system. More significantly, these fumes can be explosive and create a dangerous condition when an access cover must be removed to service the internal equipment. Other liquids can pose similar hazzards. Therefore, there are many liquids with which the apparatus described in said patent cannot be used; and this impediment is generally present just where a non-invasive measuring system is required.